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Kepler-70b (formerly known as its Kepler Object of Interest designation KOI-55.01; sometimes listed as KOI-55 b) is one of two postulated exoplanets orbiting the subdwarf B star (sdB) Kepler-70. The other planet is Kepler-70c, and both planets (if they exist) orbit very close to their host star.[1]

Kepler-70b
Artist's impression
Discovery
Discovered byCharpinet et al.[1]
Discovery siteKepler telescope
Discovery date22 December 2011 (announced) [1]
Detection method
Reflection/emission modulations
Orbital characteristics
Semi-major axis
0.006 AU (900,000 km)
Orbital period (sidereal)
5.76 hr
Inclination~65
StarKepler-70
Physical characteristics
Mean radius
0.759 [note 1][2] REarth
Volume4.736×1015 km3
Mass0.43507362784471 MEarth
Mean density
5,500 kg/m3 (9,300 lb/cu yd)
Surface gravity
7.5 m/s2
Temperature7,662 K (7,389 °C; 13,332 °F)[3][note 2]
  1. Calculated assuming an albedo of 0.1.
  2. Equilibrium temperature calculated assuming an albedo of 0.1.

However, later research[4][5] suggests that the two exoplanets probably do not exist, and that "pulsation modes visible beyond the cut-off frequency of the star" were a more likely explanation for the signals believed to indicate exoplanets. This has not been proven with certainty one way or the other.

If it exists, Kepler-70b completes one orbit around its star in just 5.76 hours, so is an ultra-short period planet. It is also the hottest known exoplanet as of mid-2017, with a surface temperature of several thousand Kelvin.[1] Its density is 5500 kg/m3 which is not much different from Earth.[6]


Characteristics



Mass, radius and temperature


Kepler-70b is likely a rocky exoplanet with a mass of 0.44 MEarth and a radius of 0.76 REarth. It has a surface temperature of over seven thousand Kelvin, the hottest known surface temperature of any exoplanet. While the precise temperature is not known, it is expected to be hotter than the surface of the Sun.[7]


Orbit


The exoplanet has an extremely short orbit, with an orbital period of 5.76 hours (345 minutes). This comes in second to the exoplanet PSR 1719-14 b, which, coincidentally, orbits a stellar remnant, much like the planets of Kepler-70.


Host star


The host star, Kepler-70 (also formally known as KOI-55, 2MASS J19452546+4105339 or KIC 5807616), is a subdwarf B-type star that left the red-giant stage of its lifetime – according to the Extrasolar Planets Encyclopedia – about 18.4 million years ago.[2] It has a surface temperature of 27730 ± 270 K, nearly 6 times as hot as the surface temperature of the Sun, which has a surface temperature of 5778 K.[8] The star has a mass of 0.496 M☉ and a radius of 0.203 R☉[note 1] It is expected to become a white dwarf in the future, after fusing the remaining helium in its core, and shrink in size to around the size of the Earth.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.87. Therefore, Kepler-70 is too dim to be seen with the naked eye.


Encounters


Kepler-70c passes 240,000 kilometres (150,000 mi) away from Kepler-70b during their closest approach, possibly causing tidal forces against each other. This is currently the closest recorded approach between planets.


Cultural impact


According to the main author of the paper in Nature that announced the discovery of the two planets, Stephane Charpinet, the two planets "probably plunged deep into the star's envelope during the red giant phase, but survived."[9] However, this is not the first sighting of planets orbiting a post-red-giant star – numerous pulsar planets have been observed, but no planet has been found with such a short period around any star, whether or not on the main sequence.


Origins


The two planets were most likely gas giants that spiraled inward toward their host star, which subsequently became a red giant, vaporizing much of the planets except for parts of their solid cores, which are now orbiting the Subdwarf B star.[9] Another theory is that only one gas giant spiralled inward into the star, and that its core fragmented inside the red giant after engulfment, with the current planets being the large core fragments.[10]


See also



Notes


  1. These statistics were very likely higher than what they were today when it was a red giant, the estimated mass of Kepler-70 before it became a subdwarf, would probably have been around 0.89–0.95 M☉.[citation needed]

References


  1. Charpinet, S.; et al. (December 21, 2011), "A compact system of small planets around a former red-giant star", Nature, 480 (7378): 496–499, Bibcode:2011Natur.480..496C, doi:10.1038/nature10631, PMID 22193103, S2CID 2213885
  2. "Notes for Planet KOI-55 b". Extrasolar Planet Database. Archived from the original on 19 January 2012. Retrieved 1 January 2012.
  3. "HEC: Exoplanets Calculator - Planetary Habitability Laboratory @ UPR Arecibo".
  4. Krzesinski, J. (August 25, 2015), "Planetary candidates around the pulsating sdB star KIC 5807616 considered doubtful", Astronomy & Astrophysics, 581: A7, Bibcode:2015A&A...581A...7K, doi:10.1051/0004-6361/201526346
  5. Blokesz, A.; Krzesinski, J.; Kedziora-Chudczer, L. (4 July 2019), "Analysis of putative exoplanetary signatures found in light curves of two sdBV stars observed by Kepler", Astronomy & Astrophysics, 627: A86, arXiv:1906.03321, Bibcode:2019A&A...627A..86B, doi:10.1051/0004-6361/201835003, S2CID 182952925
  6. "Kepler mission discoveries". Archived from the original on 27 May 2010. Retrieved 23 May 2013.
  7. S. Charpinet et al.: A compact system of small planets around a former red-giant star, Nature 480, 496–499, supplementary material (online)
  8. Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  9. "Two More Earth-Sized Planets Discovered by Kepler, Orbiting Former Red Giant Star". Universe Today. 26 December 2011. Retrieved 1 January 2012.
  10. Bear, E.; Soker, N. (26 March 2012), "A tidally destructed massive planet as the progenitor of the two light planets around the SDB star KIC 05807616", The Astrophysical Journal Letters, 749 (1): L14, arXiv:1202.1168, Bibcode:2012ApJ...749L..14B, doi:10.1088/2041-8205/749/1/L14, S2CID 119262095



На других языках

- [en] Kepler-70b

[es] Kepler-70b

Kepler-70b (antiguamente llamado KOI-55.01;[1] a veces catalogado como KOI-55 b) es un planeta descubierto orbitando la Estrella subenana de tipo B (sdB) Kepler-70. Orbita a su estrella otro planeta, Kepler-70c, ambas orbitan muy cerca de su estrella madre. Kepler-70b completa una órbita alrededor de su estrella en sólo 5,76 horas, uno de los periodos orbitales cortos de los exoplanetas descubiertos hasta ahora, sólo en segundo lugar tras PSR 1719-14 b con un período de 2,2 horas. Por lo tanto, es el exoplaneta más caliente a partir de mediados de 2013, con una temperatura superficial de 7143 K.[4] Su densidad es de 5500 kg/m³ la cual no es demasiado diferente de la de la Tierra[5]

[ru] KOI-55 b

KOI-55 b (также известна под обозначениями Kepler-70 b и KOI-55.01) — одна из двух неподтверждённых экзопланет, вращающаяся вокруг субкарлика спектрального класса B KOI-55. Экзопланета расположена примерно в 4200 световых лет (1270 парсек) от Земли[2]. Второй планетой в системе является KOI-55 c, и обе планеты (если они существуют) вращаются очень близко вокруг звезды.


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